In recent years, the digitalization of electronic equipment has been accompanied by a growing demand for reductions in the high-frequency region impedance (the equivalent series resistance: ESR) of the capacitors used in the electronic equipment. Conventionally, in order to satisfy these demands, capacitors have been used in which an oxide film of a valve metal such as aluminum, tantalum or niobium is used as a dielectric layer, and a solid electrolyte layer of a π-conjugated conductive polymer such as a polypyrrole or a polythiophene is formed on the surface of the dielectric layer.
As disclosed in Patent Document 1, the structures of these capacitors generally include an anode composed of a valve metal and having unevenness formed in the surface thereof, a dielectric layer formed by oxidizing the surface of the anode, a cathode composed of a conductor, and a solid electrolyte layer formed between the dielectric layer and the cathode.
Widely known methods for forming a solid electrolyte layer of a π-conjugated conductive polymer include electrolytic polymerization methods (see Patent Document 2) and chemical oxidative polymerization methods (see Patent Document 3).